Charge transport devices are known and commonly employed as electronic devices for communicating or creating electronic signals. Positively or negatively charged particles such as, for example, positively charged molecules, positively charged atoms, or negatively charged electrons may be transported ballistically within such devices. The charged particles typically emanate from a source within the device and are subsequently received at a terminal within the device designed to accept the particles.
In many instances the transport of charged particles within a ballistic charge transport device is aided by the presence of an electric field. As charged particles traverse an electric field, energy is transferred to the particle and is observed as a kinetic energy gain.
Particles having appreciable kinetic energy and impinging on a receiving terminal may cause undesirable emanation of similarly or oppositely charged particles from the terminal at which the desired particles are received. Oppositely charged undesired particles emanating from the receiving terminal and in the presence of the electric field will be accelerated toward the source of desired particles where they will impact on and damage the source.
Ballistic charge transport devices typically provide for transport of charged particles within an evacuated region. Desorption of adsorbed contaminants which may have been adhered to surfaces within the device will result in a degradation to the integrity of the evacuated region. Such desorption of adsorbed constituents provides an opportunity for contaminants to intrude within the region of desired charged particle trajectories (as desired charged particles traverse the region from source to receiving terminal) and to themselves become charged as a result of impact with the desired charged particles. Charged contaminates may then, under influence of the electric field, accelerate toward the desired charged particle source and cause the source to be contaminated or damaged.
It is known that by providing surface area coatings of preferred elemental solids such as, for example, titanium, barium, or zirconium oxide, within an evacuated electronic device contaminants may be selectively absorbed.
However, such coatings are not compatible with nor will they provide for the desired operation of some ballistic charge transport devices. Many such coatings are metallic conductors and, as such, unsuitable for particular applications. Further, since such coatings rely on the random motion of the contaminants the probability of absorption of contaminants by such a coating rather than impingement of the contaminant particle at the source is less than that which is desired.
Accordingly, there exists a need for a ballistic charge transport device which overcomes at least some of the shortcomings herein described.